In a manufacturing process of a semiconductor device, a semiconductor wafer (substrate) is subjected to various processes such as an oxidation process, a film deposition process, and so on. As an apparatus for performing these processes, there has been used, for example, a vertical heat processing apparatus (semiconductor manufacturing apparatus) that is capable of processing a number of wafers as a batch (see, e.g., Japanese Patent Publication No. 3378241). The vertical heat processing apparatus includes a vertical heat processing furnace having a furnace opening in a lower part thereof, and a loading area (conveyance area) formed below the heat processing furnace. In the loading area, a boat (substrate holder) for holding thereon a number of (about 100 to 150) large wafers, e.g., 300 mm wafers is placed, via a heat-retention tube, on an upper part of a lid member for opening and closing the furnace opening. In the loading area, there are also disposed: an elevating mechanism for vertically moving the lid member so as to load the boat into the heat processing furnace and to unload the boat therefrom; a conveying mechanism that conveys the wafers between a carrier (container), which can contain a plurality of wafers, and the boat; and so on.
Generally, the boat is made of quartz and thus is very expensive. The wafer(s) is also generally expensive, and a manufacturing cost for that is increased as the process proceeds. Therefore, they should be carefully handled.
However, it is difficult to provide an earthquake resistant structure and/or earthquake resistant capability to the conventional batch type of semiconductor manufacturing apparatus because many restrictions exist in terms of both hardwares and softwares. Thus, sufficient countermeasures have not been taken against an earthquake conventionally. Thus, if an earthquake happens and severely shakes the apparatus, there is a possibility that the boat turns over and/or the boat and the wafers break, resulting in a serious damage.
In order to avoid such a risk, in the vertical heat processing apparatus described in the above patent document, there is employed a structure in which a bottom plate of the substrate holder and the heat retention tube are securely connected to each other by a substrate-holder securing member.
In addition, in a vertical heat processing apparatus, it is preferable to use two boats in such a manner that, while one boat loaded in a heat processing furnace is being subjected to a heat process, the other boat is placed on a boat table and wafers are conveyed to or from the other boat. This is called “two-boat system”.
However, in a vertical heat processing apparatus adopting the two-boat system, since the one boat on the heat retention tube is replaced with the other boat, it is difficult to employ the structure as described in the above patent document, i.e., the structure in which the heat retention tube and the substrate holder are securely connected by a substrate-holder securing member.